Little is known about the etiology of individual differences in adjustment to the typical stresses of early adolescence. The purpose of the proposed research is to extend the longitudinal Colorado Adoption Project (CAP), initiated in 1975, into early adolescence. With the support of a grant from the Spencer Foundation, the adjustment of 185, 84, and 34 adopted and nonadopted children will have been assessed via telephone and questionnaire at 9, 10, and 11 years, respectively. In the proposed study, the total number of adopted and nonadopted children tested at 9, 10, and 11 will be increased to 576, 495, and 441, respectively. In addition, to test battery will be administered in our laboratory when the children are 12 years of age in order to validate the telephone test results, to administer the WISC-R IQ test, and to complete the test series for early adolescence. Importantly, these adopted and nonadopted children have been studied previously in their homes at 1, 2, 3, and 4 and in the laboratory at 7 years of age using an extensive set of psychological and environmental assessments; in addition, the biological and adoptive parents of the adoptees and parents of the matched nonadopted children have taken the WAIS-R IQ test and have completed a 3-hour battery of psychological measures. Because of the unique prospective, longitudinal design of this adoption study, the size and representativeness of its sample, its demonstrated absence of selective placement, and its low rate of attrition, the CAP has become a landmark study of the genetic and environmental origins of individual differences. For these reasons, and because such a study could not be conducted again given the drastic decline in the numbers of newborns available for adoption, it is imperative to capitalize on this opportunity to conduct the first prospective adoption study of adjustment during early adolescence.